Display screen or portion thereof with a graphical user interface



The sole FIGURE is a front view of a display screen or portion thereof with a graphical user interface, showing our new design.

The dash-dot broken lines showing a display screen or portion thereof form no part of the claimed design. The dash-dash broken lines showing portions of the graphical user interface form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface , substantially as shown and described. 